Ion implantation is a physical process that is employed in semiconductor device fabrication to selectively implant dopant into semiconductor and/or wafer material. Thus, the act of implanting does not rely on a chemical interaction between a dopant and semiconductor material. For ion implantation, dopant atoms/molecules from an ion source of an ion implanter are ionized, accelerated, formed into an ion beam, analyzed, and swept across a wafer, or the wafer is swept through the ion beam. The dopant ions physically bombard the wafer, enter the surface and come to rest below the surface, at a depth related to their energy.
Ion sources in ion implanters typically generate the ion beam by ionizing a source material in an arc chamber, wherein a component of the source material is a desired dopant element. The desired dopant element is then extracted from the ionized source material in the form of the ion beam.
Conventionally, when aluminum ions are the desired dopant element, materials such as aluminum nitride (AlN) and alumina (Al2O3) have been used as a source material of aluminum ions for the purpose of ion implantation. Aluminum nitride or alumina are solid, insulative materials which are typically placed in the arc chamber where the plasma is formed (in the ion source).
A gas is conventionally introduced (e.g., fluorine) to chemically etch the aluminum-containing materials, whereby the source material is ionized, and aluminum is extracted and transferred along the beamline to silicon carbide workpiece positioned in an end station for implantation thereto. The aluminum-containing materials, for example, are commonly used with some form of etchant gas (e.g., BF3, PF3, NF3, etc.) in the arc chamber as the source material of the aluminum ions. These materials, however, have the unfortunate side effect of producing insulating material (e.g., AlN, Al2O3, etc.) which is emitted along with the intended aluminum ions from the arc chamber.
The insulating material subsequently coats various components of the ion source, such as extracting electrodes, which then begin to build an electric charge and unfavorably alter the electrostatic characteristic of the extraction electrodes. The consequence of the electric charge build-up results in behavior commonly referred to as arcing, or “glitching”, of the extraction electrodes as the built-up charge arcs to other components and or to ground. In extreme cases, behavior of a power supply for the extraction electrodes can be altered and distorted. This typically results in unpredictable beam behavior and leads to reduced beam currents and frequent preventive maintenance to clean the various components associated with the ion source. Additionally, flakes and other residue from these materials can form in the arc chamber, thus altering its operational characteristics, leading to additional frequent cleaning.